Short wave reception



@et 25, 1938A B. TREvoR 'ET AL lSHORT WAVEREGEPTION Original Filed Dec. 6, 1935 Illll ululull Al .ENI Em M2 F unv.

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INVENTORS BERTRAM TREVOR AND ALP W. GEORGE ATTORNEY.

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Patented Oct. 25, 1938 PATENT OFFICE .2,134,590 Y sHoR'rjWAvE RECEPTION" VBertram Trevor and Ralph Waldo George, Riverhead, N. Y.,.a`ssignors to Radio Corporation of America, acorporation of Delaware Original application December 6, 1935, vSerial No. 53,136. Divided andthis application September 16, 1936, Serial' No. 100,974

L: claims. (ci. 25o- 20) rents change in frequency,` normally requiring i retuning or the use of beat frequency amplifiers having wide pass bands. Returning, obviously, is objectionable fromthe operating pointof `ViewV and use of wide pass band amplifiers' is undesirable since they increase the overall noise levelor backgroundl in theffinal receiver output. t

To overcome these disadvantages is themain object of our invention.A

This object is effected by,V utilizing the following relations of frequency-"of operation and temperature coeicient of frequency:

1. When the rst beating oscillator is operated on the high frequency side of the signal, both the rst and second beating oscillators are made to have the same sign of temperature coefficient, regardless of Which side of the first intermediate i frequency the second beating oscillator is on.

2. When the first beating oscillator is onV the low frequency side of the signal, the temperature coefficient of the first and second beating oscillators are made opposite in sign in order to have frequency compensation which will take place regardless of Which side of the first intermediate frequency the second beating oscillator is on.

Our present invention is more fully described in connection with the accompanying drawing which is a Wiring diagram of the first and second heterodynng stages of our ccpending application hereinabove referred to.

Turning to thedrawing, energy collected upon the receiving antenna 2 is fed through a coupling transformer having a primary Il and a sec- Concentrically mounted rWithin the cylinder i2 there is a rod or metal pipe i4 grounded at its left-hand end I6 and connected to ground at its right-hand end through a damping resistor I8 and variable tuning condenser 20. The metal rod I4 within the metal cylinder I2 forms a sharply selective input circuit, standing current waves being set up thereon by virtue of the input from the secondary 6 and by virtue of the tuning of condenser 20.

The received energy resonated in the rod M and condenser 20 is fed through a 10W impedance connection 22 to a second rod, tube or metallic pipe 24 mounted Within a second cylinder 26 Whichis grounded as shown. The far end of the second rod 24 is tuned by means of the variable tuning condenserv 28V. The rod. 2i and condenser 28 form a second non-radiating highly V selective circuit and adjusted to have a resonant curvevvvhich overlaps the resonant curve of Vthe rod lli-condenser 2l! combination. In this Way, the-frequency'pass band-width of the two preselector circuits i4, 2li, I2 and 24, 26, 28 is further widened.-

` r The received filtered energy is then fed to the grid of -a` first detector tube 34. This first detector is also vsupplied with heterodyning energy from a rst local oscillator comprising a discharge energy is injected into a thermo-responsive frequency compensating Vvmeans 90 and thence through the cathode leads of the detector tube 34 for producing therein a beating of the oscillator frequency with the incoming frequency collected by the antenna 2. The oscillator, itself, is tuned by means of a coil 58 and tuning condenser 60 in the plate circuit. A by-pass condenser B2 separates the plate potential lead @It from the grounded device The beat frequency energy is resonated in the plate circuit of the first detector 3a by means of a tuning coil 42 and tuning condenser 44, both of which are adjusted to the beat frequency. The beat frequency energy is fed through a by-passing condenser 56 to a first beat frequency amplifier and then fed to a second detector |34. The latter is supplied with oscillations from a second local oscillation generatorV having a discharge tube Mil and the beat frequency output from the second detector is fed into a second intermediate frequency amplifier Whose output is utilized as desired. Thefirst local oscillator and the second local oscillator are made to have temperature coefficients of frequency such that despite variations in ambient temperature, the final beat frequency energy fed to the third detector and second intermediate frequency amplifier remains substantially constant.

The structural details of the thermo-responsive frequency compensating means 90 may be in accordance with the disclosure of our aforesaid parent application, or they may be in accordance with other devices Well known in the art having as their function to stabilize the frequency of an oscillatory circuit and to render said frequency relatively independent of temperature changes.

Preferably, the second local oscillator is tuned below the frequency of the intermediatefrequency oscillations produced by the first detector 34, and the first local oscillator 48 is adjusted to produce oscillations at a frequency above the incoming wave frequency. Then, if the two local oscillators have the same or approximately the same, frequency variation with ambient temperature changes, the resultant beat-frequency in the circuit |44 will remain effectively constant despite changes in the surrounding temperature.

The same result may be obtained by having the second local oscillator` |40 tuned above the first intermediate-frequency and the first local oscillator 48 adjusted to produce oscillations of a frequency lower than the incoming wavefrequency while at the same time producing the desired beat frequencies.

To summarize, if the first beating or local oscillator is operated on the high frequency side of the signal, both beating oscillators for frequency compensation should be made to have the same sign of temperature coefficient regardless of which side of the first intermediate frequency the second beating local or heterodyning oscillator is on. On the other hand, if the first beating oscillator is on the low frequency side of the signal, frequency compensation will occur provided the ternperature coefficient of the second beating oscillator is made opposite in sign to that of the first. This latter effect will take place regardless of which side of the first intermediate frequency the second beating oscillator is on.

The desired frequency temperature coeflicient for the rst and second local oscillators may be obtained by proper choice of the materials used in their construction, particularly the materials used in the frequency controlling circuits. If

desired, the frequency controlling circuits of each oscillator may be provided with a movable tuning condenser plate which is moved in such a way by a temperature responsive bi-metallic strip that the desired changes in frequency with temperature are produced.

Having thus described our invention, what we claim is:

l. In a heterodyne receiver of high frequency waves a rst local oscillator, means for heterodyning said waves with output energy from said oscillator thereby to produce a first beat frequency, a second local oscillator, means for heterodyning Waves of said first beat frequency with output energy from said second local oscillator, thereby to produce a second beat frequency, and thermo-responsive means for so controlling the frequency relationship between the two oscillators that said second beat frequency remains substantially constant, despite variations in the ambient temperature.

2. Apparatus in. accordance with claim 1 and having the first local oscillator adjusted to a higher frequency than that of the waves with which its output energy is heterodyned, said thermo-responsive means being operable to Vary the frequency adjustments of the two said oscillators in the same direction upon the occurrence of a given change in the ambient temperature.

3. Apparatus in accordance with claim 1 and having the first local oscillator adjusted to a lower frequency than that of the waves with which its output energy is heterodyned, said thermo-responsive means being operable to simultaneously vary the frequency adjustments of the two said oscillators opposingly.

BERTRAM TREVOR. RALPH WALDO GEORGE. 

